Help me understand performance stats

Hi. I’ve just finished my first game in UE and I’m very happy about the result. Now I’m trying to optimize the game as much as possible. The game I’ve created is for android, so I’ve tested it on a Samsung Galaxy S8 and I have 60FPS but on my other device, Samsung Tab 3, I have only 25-30 FPS and I’ve tried everything to increase the fps but without any results.
I have only static lights, so no dynamic lights, no sky sphere, no directional lights. I’m using default lit for all my materials and I’m using Cull distance vol and Precomputed visibility volume. The game is happening inside a house, so first I’ve used streaming levels but I had spikes when loaded/unloaded levels so now I’m loading the entire house.
The thing is that in some corners, or when I’m facing to a specific wal,l FPS is dropping on my Galaxy S8 to 45-50 FPS and I don’t know why is that. I’ve deleted the walls but still without figuring out why.
I’m trying now to figure out the stat scenerendering and stat gpu but I don’t understand the meanings of each stat, to optimize better the game. I’ve printed 4 screens from the same corner, where my FPS is dropping down. And I’m also using Exponential fog, for a better effects.

1.0 - (With pp and fog) Here I’m using Mobile HDR on and Bloom + Exponential Fog

1.1 - (With PP and without fog) Mobile HDR and Bloom ON, but without Exponential Fog

2.0 - (withoutpp) With Without Mobile HDR and without Bloom but Exponential Fog activated

2.1 - (Withoutpp and without fog) Without Mobile HDR and without Bloom and without Exponential Fog

From this pics, where I do have the best performance and where I have the biggest costs? As you can see I’ve printed the stats from the same corner because there I have FPS drops. Also what should I do for older devices? I’m also using Device Profiles and for Android Low I’ve setted Max Lod size to 256.

Thank you!